Sverre Grimnes

Some thoughts on bioimpedance and biodielectrics

From early on we learnt that a dielectric is an insulator, and a practical way to measure it was to place it between two capacitor plates. The plates were dry and so was the dielectric – the resistance between the plates was very high. With living tissue it was quite different, the material was not dry and the capacitor plates had wet contact with the tissue. At the wet plates polarization impedance appeared constituting an important source of error. The discipline of bioimpedance had one problem more than the discipline of dielectrics. Even so it became more and more common to classify tissue as a dielectric instead of a conductor. The terms melted together, but not completely. Taking a closer look at the theory of Bioimpedance and Biodielectrics we discover that both disciplines suffer from a lack of consistency. Dielectric theory emerged much earlier than impedance theory; it started more than 200 years ago with Coulomb’s law (1795): ,